In holographic recording that utilizes holography to record information into a recording medium, an information beam and a reference beam are superposed each other in a holographic recording medium and an optical interference pattern formed by these beams is written as a diffraction grating.
As one of holographic recording systems, there is a system that modulates a recording beam comprising the information and reference beams in time and space and irradiates it to a recording medium while continuously moving the recording medium with respect to the optical axis of the recording beam. This includes, for example, a holographic recording system that irradiates the recording beam from an optical head while rotating a disc-shaped recording medium.
In this case, to prevent an aberration of the diffraction grating to be recorded in the recording medium moving relative to the recording beam, a light pulse as short as several tens nanoseconds is necessary to perform recording, causing the sensitivities in both recording and reproducing to decrease.
Alternatively, as described in, for example, Japanese Patent Laid-Open Publication No. 2002-183975, there is another holographic recording system that drives an optical head along tracks formed in the circumference direction of a disc-shaped recording medium by using an elastic arm, an electromagnetic coil, and a magnet to change the position of the recording beam.
This is the so-called stop-and-go recording method, in which recording is performed so that the variation of the relative position of the recording beam with respect to an information recording region in the recording medium will not occur when the recording medium rotates, and then the optical head is moved back to the original position while the recording beam (laser beam) turns off.
In the holographic recording system described in the above Japanese Patent Laid-Open Publication No. 2002-183975, irradiation position moving means comprising an elastic arm, an electromagnetic coil, and a magnet is provided as described above and is controlled by a follow-up control circuit so as to make the irradiation position of the recording beam follow an information recording region in the recording medium for a predetermined time and move it back to the original position. Therefore, the structure is complicated, the fabrication cost is high, and there is a risk that the recording beam cannot reliably follow the recording medium when the recording medium is rotated at high speed.